Batteries, and in particular rechargeable batteries, have a finite life due to the occurrence of unwanted chemical or physical changes to, or the loss of, the active materials of which they are made. Without the unwanted chemical or physical changes, rechargeable batteries could last indefinitely over an infinite number of charge cycles, wherein the charge cycle is defined as the complete charging and complete discharging of the rechargeable battery. The unwanted chemical or physical changes to the active materials within a rechargeable battery are usually irreversible and affect the electrical performance of the rechargeable battery or cell over time.
Battery cycle life is defined as the number of complete charge-discharge cycles a battery can perform before its full charge capacity falls below 80% of its initial full charge capacity. A battery's capacity is usually rated in milliamp hours (mAh). Two key factors that affect a battery's cycle life are change rate and a number N of charge-discharge cycles completed.
A battery cycle life of 300 to 1200 cycles is typical depending on various factors including how fast the battery is recharged. The aging process of the battery results in a gradual reduction in the full charge capacity over time. That is when a cell reaches its specific lifetime it does not stop working suddenly. Instead, the aging process continues at a rate wherein a cell or battery whose capacity had fallen to 80% after 500 cycles will probably continue working to 1000 cycles, but its effective capacity will continue to fall. Thus, there is no need to fear sudden death when a rechargeable cell reaches the end of its specified battery life.
Mobile communication devices, such as mobile phones, tablet pads, personal digital assistants (PDAs), laptop computers and the like (hereinafter user equipment (UE)) often use lithium-ion batteries. It is the nature of lithium-ion batteries and other rechargeable batteries such as nickel-metal hydride, lithium polymer, and NiCad batteries (hereinafter referred to as a “rechargeable batteries” or “batteries”) after many charge-discharge cycles of the batteries, to lose their ability to recharge to their original capacity. In other words, after many charge cycles of the battery, the battery stores or holds a lower maximum mAh.
From a user's perspective, this means that a UE having a rechargeable battery that originally operated for 18 to 20 hours between requiring a battery charge will, over time, only operate for about 14 to 16 hours before being fully discharged and requiring a battery recharge.
Presently, UEs having rechargeable batteries are designed to charge their rechargeable batteries as quickly as possible. For example, many manufacturers would like the rechargeable batteries of a UE to charge within about 1 to 2 hours. Ideally, many manufacturers want the charge time to be as short as possible so that the user waits a minimal amount of time before being able to use his fully charged UE again.
It has been found that charging a rechargeable battery at the maximum charge rate minimizes the number of charge cycles in a battery's cycle life. Alternatively, it is known that one way to increase the number of charge cycles in the cycle life of a rechargeable battery is to charge the rechargeable battery at a slower rate over a longer period of time.
What is needed is a system and method for recharging a battery in a UE and at a reduced charge rate in order to increase the number of charge cycles in the cycle life of the UE's rechargeable battery. Furthermore, what is needed is a system and method for recharging the battery in a UE at a decreased charge rate during a time period when the user is unlikely to be actively using the UE and to recharge the battery of the UE and alternatively at a maximum charge rate when the user is most inconvenienced by having to wait an extended period of time for the rechargeable battery of the UE to be recharged.